Getting the Week Number in JavaScript Like PHP's date('W')
PHP's date('W') function returns the current ISO-8601 week number of the year, starting on Monday. We can achieve the same result in JavaScript using the following approach:
Using External Library
The external library available at the following link can be used to calculate the ISO week number of a given date:
Custom JavaScript Code
Alternatively, we can implement a custom JavaScript function to calculate the week number:
/* For a given date, get the ISO week number * * Based on information at: * * THIS PAGE (DOMAIN EVEN) DOESN'T EXIST ANYMORE UNFORTUNATELY * http://www.merlyn.demon.co.uk/weekcalc.htm#WNR * * Algorithm is to find nearest thursday, it's year * is the year of the week number. Then get weeks * between that date and the first day of that year. * * Note that dates in one year can be weeks of previous * or next year, overlap is up to 3 days. * * e.g. 2014/12/29 is Monday in week 1 of 2015 * 2012/1/1 is Sunday in week 52 of 2011 */ function getWeekNumber(d) { // Copy date so don't modify original d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate())); // Set to nearest Thursday: current date + 4 - current day number // Make Sunday's day number 7 d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay()||7)); // Get first day of year var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1)); // Calculate full weeks to nearest Thursday var weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7); // Return array of year and week number return [d.getUTCFullYear(), weekNo]; } var result = getWeekNumber(new Date()); document.write('It\'s currently week ' + result[1] + ' of ' + result[0]);
Usage
var date = new Date("2018-01-15"); var weekNumber = getWeekNumber(date); console.log(weekNumber[1]); // Output: 3
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